Standards demand that assurance cases support safety critical developments. It is widely acknowledged, however, that the current practice of post-hoc assurance-that the product is built and only then argued for safety-leads to many engineering process deficiencies, extra expense, and poorer products. This paper argues how the Problem Oriented Software Engineering framework can be used in the concurrent design of a safe product and its safety case, by which these deficiencies can be addressed. The basis of the paper is a real development, undertaken by the second author of this paper, of safety-related subsystems flying in real aircraft. The case study retains all essential detail and complexity.